valve lifters/valve clearance adjustment

[galaxee]

valve lifters, in the most basic of terms, are little "buckets" that sit between the camshaft and the valve that lifts the valve up when needed in time with the rest of the engine.

here are a sampling of them:


toyota has used a series of valve lifters over the years, the first generation look like so:








note how the bucket has a shim on top of it that lifts out. this is what is used to adjust valve clearance. many different sized shims are available to adjust to a proper clearance. shims can be replaced easily by removing it from the top of the bucket.

the second generation, we don't have any buckets to give you an example. but here is a shim.


now on to the new generation, as on the prius. there are 16 of these suckers in a prius engine.




look mom, no shim! this is what makes valve clearance adjustment a serious PITA... you have to remove the whole bucket, not just the shim from the top. and to get the bucket out, you need to take the camshaft out. and to take the cam out, you have to remove the sprocket. and to remove the sprocket, you have to get the timing chain off it.... get the drift

then all 16 buckets need to be replaced with ones that have different thicknesses.

so for those of you concerned about valve adjustment- 60k is pretty early to do this and theoretically your valves shouldn't be out of adjustment yet. 100k or more is more reasonable... basically if there's a reason to go in there. as in, if your valve cover gasket starts to leak and it needs replacing anyway. around 100k is where you might start to see evidence of your seals degrading with use, so if you're having something replaced this isn't unreasonable to do at that point.

to adjust this, you do need to break that seal. and breaking engine seals unnecessarily, unless in the hands of a known competent engine gasket person, is a bad bad idea.

[paprius4030]

Is it far to say then, leave it alone till the engine acts up? Is there away to otherwise check to see if the valves are out of adjustment, like compression check or something or checking compression with compressed air like they do on little airplanes and see if air hisses out of exhaust or the intake?

[hyo silver]

I remember reading all about buckets and shims in a repair manual for my motorcycle, then opening up the engine to find screw-type adjusters. They were very fidgety and took several tries to get just right with only two hands, but it was much easier than taking half the engine apart. Dual overhead cams, four valves per cylinder, and 11,000 rpm was way cool for 1981.

[galaxee]

compression test won't tell you if your valves are out of adjustment, it will tell you if one is sticking. but it won't tell you if that's because of clearance or because they're not getting proper lifting.

so there's no way short of going in there to check the valve clearance.

valve clearance doesn't typically tighten- it gets more slack. you'd start to hear a valve lifter tick in the top end before you noticed performance issues as far as the engine 'acting up' goes.

there's actually a special tool for those screw-type adjusters now, hyo, but just the mention of said adjusters got quite the reaction out of DH

[qbee42]

<div class='quotetop'>QUOTE(galaxee @ Oct 22 2007, 10:37 PM) [snapback]529113[/snapback]</div>

there's actually a special tool for those screw-type adjusters now, hyo, but just the mention of said adjusters got quite the reaction out of DH
[/b]

We have screw type adjusters on our boat's diesel engine. The special tools for that are a large flat-blade screw driver and an a big crescent wrench. It's very delicate.

Tom

[patsparks]

Never adjusted the valves on the Camry and I'm guessing the Prius will be the same.

Thanks for the pictures though galaxee.

[David Beale]

I had the last model of Subaru with the pushrod engine. It used a special tool, with two handles. One had a hex that loosened the lock nut, the other had a hex that did the adjustment. And yes, it was very fidgety. I eventually learned the angle that compensated for the screw movement when you tightened the lock nut.

If there is a problem with the valve seat moving in the head material the valve will tighten. Otherwise, it will loosen. In my experience, -most- of the time these things don't need to be adjusted over the life of an engine. Particularly for a 5000 RPM engine. But I guess we'll see. The manufacturers always provide a lot of effort to make sure they stay in adjustment, and a lot of effort to make sure the dealers know how to do so. Even so, the anti-Prius (2001 Pathfinder with 3.5L VQ engine) never needed this service. You can usually tell it's needed if it gets noisy (so called "tappit noise"), or seems to "miss" (tight valve).

Some of the high reving motorcycle engines (and the Ford SHO engine) would have a tendency to "spit out" the shims when over-reved! Not nice!

[hobbit]

One hopes that in these engines, valve and seat wear will compensate
for bucket and cam wear. If they both happen at roughly the same
rate the whole valve will gradually sit a little higher than it used
to, but all the relative clearances will still be the same!
.
_H*

[apriusfan]

Whatever happened to hydraulic valve tappets?

[qbee42]

<div class='quotetop'>QUOTE(apriusfan @ Oct 25 2007, 01:45 PM) [snapback]530338[/snapback]</div>

Whatever happened to hydraulic valve tappets?
[/b]

They tend to float at high speeds.

Tom